Valve is opening up a new revenue stream on its popular Steam service by allowing its players to buy and sell virtual goods.

The Steam Community Market began a beta period on Wednesday, currently applicable only to Valve's premiere free-to-play game, Team Fortress 2.

What does this mean for game developers? Potentially, a new source of revenue. While Valve will pocket 5% of the revenue from these virtual sales (to recoup "nominal fraud incidents"), the company says there is also an additional game-specific fee for each transaction, which is determined and collected by the individual game's publisher. Currently that fee is 10 percent for Team Fortress 2.